text: The I-Xe system was first applied in 1975 to estimate the age of the Earth. For all Xe isotopes, the initial isotope composition of iodine in the Earth is given by
  where  is the isotopic ratios of iodine at the time that Earth primarily formed,  is the isotopic ratio of iodine at the end of stellar nucleosynthesis, and  is the time interval between the end of stellar nucleosynthesis and the formation of the Earth. The estimated iodine-127 concentration in the Bulk Silicate Earth (BSE) (= crust + mantle average) ranges from 7 to 10 parts per billion (ppb) by mass. If the BSE represents Earth's chemical composition, the total I in the BSE ranges from 2.26×10 to 3.23×10 moles. The meteorite Bjurböle is 4.56 billion years old with an initial I/I ratio of 1.1×10,  so an equation can be derived as
  where  is the interval between the formation of the Earth and the formation of meteorite Bjurböle. Given the half life of I of 15.7 Myr, and assuming that all the initial I has decayed to Xe, the following equation can be derived:
  Xe in the modern atmosphere is 3.63×10 grams. The iodine content for BSE lies between 10 and 12 ppb by mass. Consequently,  should be 108 Myr, i.e., the Xe-closure age is 108 Myr younger than the age of meteorite Bjurböle. The estimated Xe closure time was ~4.45 billion years ago when the growing Earth started to retain Xe in its atmosphere, which is coincident with ages derived from other geochronology dating methods.